1. Field of the Invention
Exemplary aspects of the present invention relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium, and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
The fixing device used in such image forming apparatuses may employ a fixing belt, formed into a loop, to apply heat to the recording medium bearing the toner image, and a pressing roller, disposed opposite the fixing belt, to apply pressure to the recording medium. A stationary, nip formation pad disposed inside the loop formed by the fixing belt is pressed against the pressing roller disposed outside the loop formed by the fixing belt via the fixing belt to form a nip between the fixing belt and the pressing roller through which the recording medium bearing the toner image passes. As the fixing belt and the pressing roller rotate and convey the recording medium through the nip, they apply heat and pressure to the recording medium to fix the toner image on the recording medium.
As a mechanism that heats the fixing belt, the fixing device may include a substantially tubular metal member disposed inside the loop formed by the fixing belt and a heater disposed inside the metal member to heat the metal member, which in turn heats the fixing belt. In addition, the nip formation pad pressed against the pressing roller may be supported by a pad support disposed inside the metal member. Since the pad support is disposed opposite the heater, it is given a finish that locally or entirely reflects heat emitted by the heater to cause the reflected heat to irradiate an inner circumferential surface of the metal member, thus using the heat striking the pad support for effective heating of the metal member.
The above-described configuration is generally effective, and in part relies on the passage of recording medium through the nip to draw off the heat thus generated. However, a problem arises when relatively small recording media having a smaller width in the axial direction of the fixing belt are conveyed to the nip continuously. In that case, the lateral end portions of the fixing belt in the axial direction thereof may retain an excessive amount of heat because the small recording media do not pass through the lateral end portions of the fixing belt and therefore do not draw heat therefrom, resulting in overheating of the lateral end portions of the fixing belt and the corresponding sections of the metal member disposed opposite the lateral end portions of the fixing belt. Consequently, the fixing belt and the metal member may suffer from thermal damage.